re-motoring a Presto 6n

[JayDC]

Hey Guys,
Does anyone have any recommendations on a motor and a good idea on how to convert my Presto 6n to a direct drive turntable? I'd love to have variable speeds 33,45,78 don't care if its push button or something i have calibrate with a strobo.. So I'm guessing i need a motor, a speed controller, and away to directly mount the motor to the shaft of the platter..

[JayDC]

nobody has done something like this ans is willing to share the information?

[petermontg]

am sure someone has done this before

if you contact gib epling @ westtech.com

he restores vintage gear and espically presto gear

[markrob]

Hi,

Here ia a link to a mod Flo did sometime ago

http://www.floka.com/lofi/portable_lathe.html

This is not easy, but doable if you have money and some skills.

Mark

[cymbalism]

I want to see how the motor drives the platter. Is he doing it with a belt or some sort of mechanism that still drives the inside of the platter

[markrob]

Hi,

Its a rubber belt drive. You can see it in the frist phot. Also, he indicated in his caption that he used a 3mm round belt made of sealing wire.

Mark

[JayDC]

oh yeah... duh, i forgot that flo did that.. I wanted to know in the past if that head would fit the 6n overhead, as he did that to prove it would.. Awesome creation i have to say.. Somewhere on this site is a thread with the drawings of the adapter that he made to fit he head, if you ever need it.


So thats the motor I need, and I suppose I'll use the belt around the lower lip of the platter.. Not Direct Drive, but quiter then the idler wheels i suppose..

http://www.premotec.com/pdf/brushless/BL58%20EB-50%20Watt%20%28high%20torque%29.pdf

[JayDC]

Found this nifty little page while researching:

http://www.rstaudio.de/TTMD/acmd_en.html

It's a complete set plans for a belt drive turntable motor and speed controller. Looks to be heading in the right direction.

Just can't really find much information on the motor of choice [embpapst VARIODRIVE Compact VDC-3-43.10] in this particular project. All i found is that this motor is 35 watts max, and the motor flo used is 50 watts max. Not sure if this motor is strong enough, and i don't know if this speed control will work with the other motor.

It's a cool speed controller though, since it has a speed sensor built in it to give you a real time digital read out of the exact speed of the turntable.

Starting to think it would be easier [for me, lol] to just go to the local hobby shop and get a strong motor and speed control for a RC car. Although they are noisy. The idea is to have a more stable speed, and a quieter motor.

I'd really like to get some people to discuss this with me, especially those whom know more about this then me to help point me more in the the right direction.

[cymbalism]

Well there it is, guess I need to pay more attention! Hehe

[markrob]

Hi,

As a first pass, you might want to consider going with a simple AC fixed speed induction motor. Just change the speeds by moving the belt to different diameters on the shaft pully. You can always upgrade to either a permanent magnet or brushless DC servo later.

Here isn a link to a nice app note on using microcontrollers for DC brushless use:

http://ww1.microchip.com/downloads/en/AppNotes/00857a.pdf

If you don't want to get involved in firmware, here is an easy to use controller from ON Semi:

http://www.onsemi.com/pub_link/Collateral/MC33035-D.PDF

You can add this chip for servo control without the need for Hall Sensors:

http://www.onsemi.com/pub_link/Collateral/MC33039-D.PDF


Mark

[JayDC]

yeah, I was originally thinking AC motor, and light dimmer...

I think i want to go with a DC motor though, i have read that unstable currents can effect AC motor speeds, while DC motors don't have this issue since the input voltage is stabilized via the power supply..

I want a very stable motor system. No wow and flutter please..

Didn't realize that the motor / speed control system i posted above drives a 28kg heavy ass piece granite as the platter. So its probably strong enough to spin the presto aluminum platter.

Although, I think you need the software for the micro controllers in his design, that is not posted..

@FLO

What did you use to control the speed of the premotec motor?

[markrob]

Hi,

A light dimmer is out with an AC induction motor. You need a variable frequency drive to control the speed. However, there is no need for this. Just pick a good synchronous motor, use the proper gearing ratios and you'll have very good speed stability. It was not until recent times that DC servo belt and direct drives were used in turntables. The motor that was originally in your Presto was an AC synchronous motor and it works fine. The bigger issue with wow and flutter is your mechanical system and the sizing of the motor in realtion to the load. Keep in mind that in the case of a turntable, a heavy platter does not have a big effect on total static load. Also, the drag on the platter by the playback pickup is very small compared with a cutter. With good bearings, you don't need much torque in a playback system other than that required to get the platter get up to speed in a reasonable amount of time due to system interia. The drive in your link may work fine for playback, but be marginal for cutting. I would go with a motor size >= that was used in the Presto. Bigger is better here. If I get a chance, I'll look at my 6N and give you the details off of the motor rating plate.

Mark

[JayDC]

i'm pretty sure that the presto motor is 1/2hp..

I suppose i could use the OG motor, and just drop the idler wheels.. its the rim drive that adds the most rumble to the cut, and the fact that the motor hums.. I think this is the sound of electricity, the 60 hz..

I'm just worried about unstable current, effecting the speed of the motor during the cut.. whats more cost effect, new motor and controller or power conditioning, i don't know..

I feel like using more then one pulley will be hard to initially figure out, once its setup it would be solid, if i use kevlar bands to drive the platter.

A speed knob will require a manual adjust and a strobo check every use, but is a little more flexible in the speed choices..

[JayDC]

Starting to wonder if it would be better to use a technics sp-15 as the turntable, and motorize the overhead. It would be a shame to not use the excellent presto platter.

Kind of thinking also I could use an aluminum block as a base, drill a hole to mount the platter on a bearing. Then figure out the proper pulleys i'd need and the spacing to get the speeds i want, and drive the turntable from the bottom post, using the original motor. Not sure how to do that math though..

[subkontrabob]

[embpapst VARIODRIVE Compact VDC-3-43.10]

there is a typo, the company's name is "EBM Papst", it's just a few km away from my place. A friend had an internship there in conjunction with his master thesis.

It's a reputable company that manufactures high quality product, most notably electric fans and motors.

If you email them I'm sure they will provide you with more information.

http://www.ebmpapst.com/en/

[mossboss]

Hi all
Am I right to say that there is a post here some time back with all the details about a Pabst motor used specifically for cutting including all the controls?
Someone surely must remember
It may have been Flo????
Cheers

[markrob]

Hi JayDC,

I had a chance to look at my Presto 6N motor today. Its a Bodine model NYC-34. The rating plate indicates 50/60hz 1500/1800 RPM. 1.0 Amp 1/25 HP. Uses A 3.75uf capacitor. So, you are off by a factor of ten on the 10 required HP.

Mark

[mossboss]

Here is Flo's quick and dirty speed control link
https://lathetrolls.com/viewtopic.php?t=1949&highlight=motors&mforum=lathetrolls
Cheers